Re: Bit datatype performance?

On Sep 14, 2011, at 6:00, Antonio Vieiro <antonio(at)antonioshome(dot)net> wrote:

> Hi all,
>
> One of my entities 'E' may be 'tagged' with an arbitrary set of 256 tags 'T'.
>
> A first approach could be to add a M:N relationship between 'E' and 'T'.
>
> A second way to do this could be to add a BIT(256) datatype to 'E',
> setting bits to '1' if the entity is tagged with each one of the 256
> tags (i.e. using a 'bitmask' on the set of tags).
>
> Since querying entities 'E' with a certain set of tags 'T' must be
> very fast I was wondering if the second approach would be faster. What
> do you think?
>
> Thanks for any hints,
> Antonio
>
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Dealing with 256 arbitrary ones and zeros instead of meaningful named tags seems to be asking for mega-confusion.

If performance is really that important do both and run some performance tests.

If the tag set ever changes a schema change will be needed for the bit version but not the two-table version.

David J.